/Engine/Plugins/Importers/USDImporter/Source/UnrealUSDWrapper/Public/UnrealUSDWrapper.h
These include the extensions for the file formats built into USD as well as those for any other file formats introduced through the USD plugin system (e.g. "abc" for the Alembic file format of the usdAbc plugin).
static [TArray](API\Runtime\Core\Containers\TArray)< [FString](API\Runtime\Core\Containers\FString) > GetAllSupportedFileFormats()